In recent years, a large-scale integrated circuit (LSI) formed in such a manner that many transistors and resistances are connected as an electric circuit and integrated on one chip has been frequently used for an important portion of computers and communication apparatuses. In particular, with regard to a semiconductor memory, the increase of memory capacity thereof is in demand in accordance with the expansion of application products. For example, a nonvolatile high-density semiconductor memory typified by a flash memory is used for an SD card, a USB memory and an SSD (Solid State Drive).
Such a nonvolatile high-density semiconductor memory is produced in the following manner. First, a memory device and a peripheral circuit are formed on a silicon semiconductor substrate. Next, the back surface of this silicon semiconductor substrate is shaved by mechanical polishing and Chemical Mechanical Polishing (CMP) to make the silicon semiconductor substrate into a thin layer. In addition, the thin-layered silicon semiconductor substrate is laminated by plurality and mounted.
In order to assure the reliability of such a high-density semiconductor memory, the impurity concentration such as metal, oxygen and carbon, and the density of crystal defects such as atomic vacancy and interstitial atoms in the silicon semiconductor substrate are controlled to a very small degree; such a silicon semiconductor substrate is produced by a semiconductor wafer maker as a high-quality silicon semiconductor substrate, which is expensive.